1. Field of the Invention
This invention relates to jet powered watercraft, especially personal watercraft (xe2x80x9cPWCxe2x80x9d). More specifically, the invention relates to a jet power assembly, in particular to an impeller and its associated components.
2. Description of Related Art
Jet powered watercraft have become very popular in recent years for recreational use and for use as transportation in coastal communities. The jet power offers high performance and allows the watercraft to be more compact and fast. Accordingly, PWCs, which typically employ jet propulsion, have become common place, especially in resort areas.
A typical jet propulsion system for a PWC includes a jet pump. The jet pump pulls water in through an inlet, pressurizes it, and forces it through a venturi resulting in a high pressure water jet. The result is a reaction force called thrust that propels the PWC in the direction opposite to the water jet. Typically, a steering nozzle, located at the discharge end of the pump, is controlled by a steering mechanism to redirect the water jet so as to effect steering of the PWC. The jet pump utilizes an impeller, rotated by an engine via a drive shaft (and/or impeller shaft) to circulate and pressurize the water. However, the typical impeller utilizes impeller blades that have a relatively large pitch. Accordingly, as the impeller is rotated, the water stream exiting the impeller is directed into a relatively tight spiraling flow. In order to rectify or straighten the spiraling water stream, the typical jet pump includes a non-rotating stator having blades to attenuate or eliminate the rotation of the flow.
FIG. 14 shows a conventional jet pump, which can be used in a jet-propelled watercraft, indicated at 800. The jet pump 800 includes a rigid housing 802 within which a stator 804 is fixedly mounted. An impeller 806 is rotatably mounted to the stator 804 via an impeller shaft 808. As shown, the impeller 806 includes a plurality of impeller blades 810. The stator 804 includes a plurality of stator vanes 812. A pump cover 814 is fastened to a rearward end of the stator 804 with, e.g., fasteners 816. A venturi 818 is connected to the housing 802 rearward of the stator 804. The connecting element 808 is fixedly connected to the impeller 806 and rotates with the impeller 806 relative to the stator 804 on bearings 820. The bearings 820 are disposed within a cavity 822 within the stator 804, which is typically filled with a lubricant. A seal 824 prevents debris and water from entering the cavity 822. The pump cover 814 protects the impeller shaft 808 and bearings 820 and encloses the cavity 822 to prevent lubricant leakage. The pump cover 814 is conically configured to facilitate the flow of water through the venturi 818. The venturi 818 sometimes includes a plurality of fins 826 therein that extend radially inwardly therefrom.
In operation, an engine is coupled to the impeller 806 via a drive shaft (not show) to thereby rotate the impeller 806. The impeller 806 thus pulls water from the body of water and pressurizes the water as the impeller 806 is rotated. Due to the rotational speed of the impeller 806 and to the pitch of the blades 810, water being pressurized by the impeller 806 assumes a spiraling flow as it exits the impeller 806. The stator vanes 812 extend relatively co-extensively to the axial direction of the jet pump 800 and serve to straighten or rectify the spiraling flow of water as it passes therethrough. The flow of water is accelerated in a progressive manner as the flow travels axially past the impeller 806 due to the progressive increase in diameter of the impeller hub 811. The flow of water exits the stator 804 and enters the venturi 818. A gradual reduction in diameter of the venturi 818 serves to converge the flow of water and also accelerates the flow. The venturi 818 includes an outlet opening 828 through which the flow of water exits the jet pump 800 to propel the watercraft.
FIG. 15 shows the stator 804 in relatively greater detail. As shown, each of the stator vanes 812 is curved to facilitate rectification of the flow of water from the impeller 806. Additionally, each of the vanes 812 has a cross-sectional configuration similar to that of an airfoil with a trailing edge that is slightly tapered. The airfoil-like configuration serves to facilitate flow of water past the stator vanes 812. However, the stator vanes 812 have a relatively constant thickness, typically about 2-5 mm. Since the stator vanes 812 are angled at their leading edge and progressively straighten out toward their trailing edge, and a flow area between the blades at the trailing edge portions is greater than a flow area between the blades at the leading edge portions, the flow of water decelerates as it moves past the vanes 812. The venturi 818 and pump cover 814 are tapered in their cross-sectional configurations so as to converge and pressurize the water stream and, therefore, the water stream is accelerated as it flows past. However, the deceleration of the water flow through the stator 804 represents an energy loss that decreases the efficiency of the jet pump 800.
FIG. 16 shows an improved type of jet pump 850, which is referred to as a converging type jet pump. As shown, the jet pump 850 has a housing 852 that incorporates an integral venturi 854. The jet pump 850 includes a stator 856 that has a plurality of stator vanes 858. A hub 860 of the stator 856 has a conical configuration corresponding to that of the venturi 854. The stator vanes 858 have an airfoil-like configuration similar to those shown in FIG. 15, but may be arranged with a greater degree of curvature. Additionally, the stator vanes 858 are also tapered (radially with respect to the stator hub 860) to conform to the venturi 854. Contrary to the stator 804 shown in FIG. 15, head loss through the stator 856 is reduced, since the cross-sectional area of the flow path between the stator vanes 858 is decreased due to the tapered configuration of the venturi 854 along the length of the vanes 858, even though trailing edge portions of the vanes 858 are narrower than the leading edge portions thereof. This design effectively eliminates the degrading head loss within the stator 856. However, typical manufacturing processes for producing stators, i.e., casting, may not be used or is highly costly due to the conical shape of the hub 860 and configuration of the vanes 858. Therefore, other more costly and inefficient methods of manufacture must be used to create the stator 856.
For at least these reasons, a need has developed for a jet pump that is highly efficient and is easily manufactured.
Another consideration with operation of PWCs is the creation of noise pollution during the operation thereof. The use of internal combustion engines operating at high RPMs make conventional watercraft typically quite noisy to operate. Technological advances in engine noise attenuation systems have dramatically decreased the operating volume of the engine in typical PWCs. Accordingly, now, noise from the jet pump of the jet propulsion system is a greater concern. In particular, an impeller of the jet pump is rotated at a relatively high RPM to generate sufficient power for the PWC. The interaction of the spatially non-uniform velocity distribution at the impeller discharge with the stator vanes of the stator causes lift and drag fluctuations on the stator vanes and flow fluctuations within the stator vane passages. In addition, the periodic blockage of the flow in the impeller blade passages by the stator vanes will result in similar force fluctuations on the impeller blades and also in flow pulsations within the blade passages. Fluctuating forces may be transmitted directly through the fluid or through the vibrational response of the structure (lift fluctuations causing a net axial force component exciting the hub at the pump attachment location). Rotor-stator interaction noise is often called xe2x80x9cinteraction tonesxe2x80x9d and can represent a relatively substantial level of noise. This is especially true when the relative rotational speed of the impeller and the stator reaches a critical frequency, wherein multiple fluctuating forces are simultaneously produced by multiple impeller blades simultaneously passing respective stator vanes.
Conventional designs of stators, e.g., stator 804 shown in FIG. 17, have oriented the stator vanes 812 at equal distances apart from one another, e.g., 10 vanes at 36xc2x0 apart. Accordingly, as illustrated in FIG. 18, at a critical frequency (cf), based on the relative numbers and speeds of the impeller blades and stator vanes, the volume level (dB) of the jet pump reaches a maximum (dBmax). There are also noise level spikes (dBh1-dBh4) at the subsequent harmonic frequencies (cfh1-cfh4) of the critical frequency.
There is therefore a need in the art to provide a jet pump that operates at lower noise levels, or that at least reduces the critical frequencies, since the noise generated at these frequencies is more irritating to the human ear.
Furthermore, another concern in operating a PWC is to prevent engine failure due to pump failure. When a jet pump fails during operation of the PWC, the pump bearings often get damaged due to the loads and high rotational speed and can no longer take up the axial thrust generated by the impeller, which is then transferred to the engine via the drive shaft connected to the impeller. The transfer of a significant axial load to the engine by the drive shaft is undesirable.
There is thus a need to prevent the transfer of the axial thrust caused by jet pump failure to the engine.
One aspect of the invention is directed to a jet pump for a watercraft comprising a generally cylindrical housing, an impeller having a hub, a plurality of impeller blades mounted on the hub, and a shaft extending from the hub for connection to a rotatable drive shaft. The impeller is disposed within the housing so as to rotate within the housing when driven by the rotatable drive shaft. A stator has a plurality of vane structures extending generally radially outwardly therefrom and extending axially therealong. The impeller is rotationally connected to the stator to allow relative movement therebetween. A coupling structure is coupled to the shaft, wherein the coupling structure has an elongated configuration including a socket having a mouth configured to receive the drive shaft and a bore disposed on an opposite side of the socket than the mouth so as to allow relative axial movement between the impeller and the drive shaft.
In accordance with another aspect, the invention is directed to a jet pump for a watercraft comprising a generally cylindrical housing having a forward portion and a rearward portion thereof, an impeller having a plurality of impeller blades mounted thereon, the impeller being disposed within the forward portion of the housing and being configured to be connected to a rotatable shaft so as to be rotatable within the housing, and a stator fixedly mounted within the housing adjacent to and rearward of the impeller. The stator has a plurality of circumferentially spaced first vane structures extending generally radially outwardly therefrom, extending axially along the stator, and tapered in width axially toward the impeller. A pump cover is fixedly mounted to a rearward side of the stator and has a plurality of circumferentially spaced second vane structures extending generally radially outwardly therefrom, extending axially along the pump cover, and tapered in width opposite the first vane structures. Each of the plurality of first vane structures abuts a respective one of the plurality of second vane structures. The pluralities of abutting first and second vane structures define a plurality of stator vanes extending axially along the stator and the pump cover and being positioned rearward of said impeller.
In accordance with another aspect, the invention is directed to a jet pump for a watercraft comprising a generally cylindrical housing having a forward portion and a rearward portion thereof and an impeller having a plurality of impeller blades mounted thereon. The impeller is disposed within the forward portion of the housing and is configured to be connected to a rotatable shaft so as to be rotatable within the housing. A stator is fixedly mounted within the housing adjacent to and rearward of the impeller. The impeller is configured to be rotationally coupled to the stator to allow relative rotational movement therebetween. The stator has a plurality of circumferentially spaced vanes extending generally radially outwardly therefrom and extending axially along the stator. Each of the vanes has a thickened intermediate section disposed between a pair of opposed ends that taper from the thickened intermediate section.
A further aspect of the invention is directed to a stator for use in a jet pump having an impeller rotatably coupled with respect to the stator, comprising a central hub portion, and a plurality of stator vanes extending outward from the central hub portion arranged with irregular spacing between adjacent vanes. At least one stator vane is spaced from an adjacent stator vane a different distance than that stator vane is spaced from its other adjacent stator vane.
An additional aspect of the invention is directed to an impeller for use in a jet pump having a stator fixed with respect to the impeller, comprising a central hub portion connected to a drive assembly to rotate the central hub portion, and a plurality of impeller blades extending outward from the central hub portion arranged with irregular spacing between adjacent blades. At least one impeller blade is spaced from an adjacent impeller blade a different distance than that impeller blade is spaced from its other adjacent impeller blade.
The jet pump in accordance with all of the embodiments of the present invention is preferably used in combination with a watercraft.
Preferably, the watercraft is a personal watercraft (PWC). The PWC can be a straddle type seated PWC or a stand-up PWC. Additionally, the watercraft could be different types of jet powered watercraft, such as a jet boat. The invention is directed to a jet pump, however, and is not intended to be limited to a watercraft.
These and other aspects of this invention will become apparent upon reading the following disclosure in accordance with the Figures.